The best-known constituent of gastric juice is hydrochloric acid, which is produced by parietal cells. The secretion of hydrochloric acid is triggered by at least three different stimuli: gastrin, histamine (H2), and acetylcholine. Receptors for these molecules are located on the surface of parietal cells. The extent of hydrochloric acid secretion appears to be a function of a complicated additive or multiplicative interaction of receptor signals of each sort. For example, a low level of any one of the hydrochloric acid stimuli results in minimal secretion, but when small amounts of all three substances are present in the stomach at the same time, secretion is very strongly stimulated.

In the digital image above, a rat stomach tissue section excised from the pylorus region is presented that was labeled with the fluorophore Oregon Green 488 conjugated to wheat germ agglutinin, targeting the Golgi network. The sample was also labeled with Alexa Fluor 568 conjugated to phalloidin and Hoechst 33342, which target filamentous actin and nuclear DNA, respectively. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.